Multi-line key telephones, also referred to as "trader turrets", are commonly used in rapid communication networks such as trading operations in banks, brokerage houses and other financial institutions. Timing is often paramount in effective trading of securities and commodities and therefore brokers must have almost instant access to traders. This is accomplished by key telephone networks wherein each broker has a key telephone with a separate line key for each trader he is likely to contact. By actuating a single line key the broker is in direct line contact with the trader. Key telephones typically have between 24 and 120 line keys. A key telephone system is described in U.S. Pat. No. Re. 31,144 "MULTI-STATION TELEPHONE SWITCHING SYSTEM" issued to Interconnect Planning Corporation of New York.
Since the key telephones can be quite large and expensive due to the large number of line keys, it is sometimes desirable to construct a key telephone with multiple talk paths, i.e., with two or more separate handsets. With a dual talk path arrangement, the key telephone is placed between two users who share a common key field to select connections for their individual handsets.
In the past such multiple telephones have existed in dual talk path (DTP) configuration with a toggle controlled "split field" switch arrangement wherein one handset or the other is coupled to the key field depending upon the position of the toggle switch. In a DTP system the user must first check the toggle position of the split field switch and, if in the wrong position, must actuate the switch to transfer control to his handset. Thereafter actuation of a line key connects the users handset to the line corresponding to the actuated line key.
Auxiliary talk paths (ATP) arrangements have also existed wherein one hand set is designated the primary talk path and the other handset is designated the auxiliary talk path. In ATP arrangements the primary handset is normally coupled to the key field. If the user of the auxiliary talk path wants a line connection he must first actuate an access key to momentarily transfer control to his handset and then actuate a selected line key.
The problem with both of these prior systems is the high likelihood of an accidental disconnect. In trading operations, often involving millions of dollars, an accidental line disconnect can have serious consequences. The problem arises when one of the users hits a line key when the key field is connected to the other user's handset. Instead of connecting his handset to a new line, he actually disconnects the other handset and connects the other handset to a new line. In the DTP arrangement this occurs when a user fails to properly set the split field toggle switch prior to hitting a line key. In the ATP arrangement the accidental disconnect occurs when the user of the auxiliary handset fails to hit the access key prior to actuating a line key.
An object to this invention is to provide a multiple talk path system which safeguards against accidental disconnects.